1. Field of the Invention
The disclosure generally relates to wideband distributed amplifiers. More specifically, the disclosure relates to a method and apparatus for providing high-speed, low signal power amplification using superconducting technology.
2. Description of Related Art
A well-known wideband amplifier known as a distributed amplifier amplifies the incoming signal to an output signal commensurate with the desired amplification level. Distributed amplifier architecture introduces delay to achieve wideband characteristics. Conventional distributed amplifiers include a pair of transmission lines, each having a characteristic impedance, for independently connecting the inputs and outputs of several active devices.
FIG. 1 shows the circuit diagram for a conventional distributed amplifier (“DA”). In FIG. 1, input signal 100 is directed to a first transmission line 110 having impedances ZI-1 to ZI-5. The amplified output signal 190 is provided by the transmission line 120 which includes impedances ZO-1 to ZO-5. In the embodiment of FIG. 1, active devices are modeled as field effect transistors (“FET”) Q1, Q2, Q3 and Q4. As the input signal 100 propagates down the input transmission line 100, each FET responds to the forward-traveling input step by inducing an amplified forward-traveling wave on the output transmission line 120. The number of active devices defines the number of stages for the DA. The amplifier of FIG. 1, shows 4 stages.
The gain of the distributed amplifier is additive rather than multiplicative. The gain is determined, in part, by the number of stages. This property enables the distributed amplifier to provide a gain at frequencies beyond that of the unity-gain frequency of any individual stage. The delays of the input transmission line 110 and the output transmission line 120 can be made equal through the selection of propagation constants and line lengths to ensure that the output signals from each individual device sums in phase. Both input and output lines must be resistively terminated, by resistors 130 and 140. A major drawback of the conventional distributed amplifier is poor efficiency because power matching and phasing cannot be achieved at the same time.
A conventional distributed amplifier is also inoperable with high-speed superconducting systems. Superconductor digital circuits feature high clock rates (i.e., 10-40 GHz) and extremely low signal power levels (i.e., 2-8 nW). Superconductor circuits are ideally suited for mixed-signal applications such as analog to digital conversion due to high sample rates and quantum accurate feedback distributed amplifiers, which use the same operating principles as the metrological voltage standard. However, because signal levels are so low and data rates are so high, establishing data links to conventional electronics, at low bit error rate, has been proved difficult.
Therefore, there is a need for a method and apparatus to provide a distributed amplifier adapted to high clock rates and low signal power.